If I get a Drobo and (2) 1 TB drives, does one back up to the other in case of failure? I am getting an ATV and want to build an iTunes server. I need a way to store big amounts of data, back it up easy, and stream. I wasn't sure if the drives mirrored so that if one fails I still have my data. Or should I just go with a couple of ministacks (much cheaper) and backup one to the other?